My experience of my mums GP ,is that you cannot. Doctors will only see him if he makes the appointment himself. Maybe in the sober moments you might be able to persuade him. You do have to ask yourself, What do I want for the Doctor?
He process for getting a Dementia assement and diagnosis is long and tiring. How likely is it that he will co-operate, with answering the questions, drawing the clock, repeating the word lists etc?
Assuming that you get the diagnosis, what then? Will he take his medication , allow carers into his home. I don't mean to sound so negative, but when dealing with the elderly, we feel we should be doing something.
Getting something done, will definitely take its toll on you.
If however you do go down this route there is something that will really help. Which is to make your self a file and note all of the following
DOB, place of birth, date of marriage, NI number, doctors full details, medication list.
In the file write down the telephone number and full name of everyone you speak to and the date and time. Also what was agreed. This is because nothing gets done with one phone call. Promises are broken people do not call back. Staff change.
Sorry that this has turned into any essay.